Windows PowerShell Error Records

Artikel
09/17/2021

Cmdlets must pass an System.Management.Automation.ErrorRecord object that identifies the error condition for terminating and non-terminating errors.

The System.Management.Automation.ErrorRecord object contains the following information:

The exception that describes the error. Often, this is an exception that the cmdlet caught and converted into an error record. Every error record must contain an exception.

If the cmdlet did not catch an exception, it must create a new exception and choose the exception class that best describes the error condition. However, you do not need to throw the exception because it can be accessed through the System.Management.Automation.ErrorRecord.Exception property of the System.Management.Automation.ErrorRecord object.

An error identifier that provides a targeted designator that can be used for diagnostic purposes and by Windows PowerShell scripts to handle specific error conditions with specific error handlers. Every error record must contain an error identifier (see Error Identifier).
An error category that provides a general designator that can be used for diagnostic purposes. Every error record must specify an error category (see Error Category).
An optional replacement error message and a recommended action (see Replacement Error Message).
Optional invocation information about the cmdlet that threw the error. This information is specified by Windows PowerShell (see Invocation Message).
The target object that was being processed when the error occurred. This might be the input object, or it might be another object that your cmdlet was processing. For example, for the command remove-item -recurse c:\somedirectory, the error might be an instance of a FileInfo object for "c:\somedirectory\lockedfile". The target object information is optional.

Error Identifier

When you create an error record, specify an identifier that designates the error condition within your cmdlet. Windows PowerShell combines the targeted identifier with the name of your cmdlet to create a fully qualified error identifier. The fully qualified error identifier can be accessed through the System.Management.Automation.ErrorRecord.FullyQualifiedErrorId property of the System.Management.Automation.ErrorRecord object. The error identifier is not available by itself. It is available only as part of the fully qualified error identifier.

Use the following guidelines to generate error identifiers when you create error records:

Make error identifiers specific to an error condition. Target the error identifiers for diagnostic purposes and for scripts that handle specific error conditions with specific error handlers. A user should be able to use the error identifier to identify the error and its source. Error identifiers also enable reporting for specific error conditions from existing exceptions so that new exception subclasses are not required.
In general, assign different error identifiers to different code paths. The end-user benefits from specific identifiers. Often, each code path that calls System.Management.Automation.Cmdlet.WriteError or System.Management.Automation.Cmdlet.Throwterminatingerror* has its own identifier. As a rule, define a new identifier when you define a new template string for the error message, and vice-versa. Do not use the error message as an identifier.
When you publish code using a particular error identifier, you establish the semantics of errors with that identifier for your complete product support lifecycle. Do not reuse it in a context that is semantically different from the original context. If the semantics of this error change, create and then use a new identifier.
You should generally use a particular error identifier only for exceptions of a particular CLR type. If the type of the exception or the type of the target object changes, create and then use a new identifier.
Choose text for your error identifier that concisely corresponds to the error that you are reporting. Use standard .NET Framework naming and capitalization conventions. Do not use white space or punctuation. Do not localize error identifiers.
Do not dynamically generate error identifiers in a non-reproducible way. For example, do not incorporate error information such as a process ID. Error identifiers are useful only if they correspond to the error identifiers seen by other users who are experiencing the same error condition.

Error Category

When you create an error record, specify the category of the error using one of the constants defined by the System.Management.Automation.ErrorCategory enumeration. Windows PowerShell uses the error category to display error information when users set the $ErrorView variable to "CategoryView".

Avoid using the System.Management.Automation.ErrorCategory NotSpecified constant. If you have any information about the error or about the operation that caused the error, choose the category that best describes the error or the operation, even if the category is not a perfect match.

The information displayed by Windows PowerShell is referred to as the category-view string and is built from the properties of the System.Management.Automation.Errorcategoryinfo class. (This class is accessed through the error System.Management.Automation.ErrorRecord.CategoryInfo property.)

{Category}: ({TargetName}:{TargetType}):[{Activity}], {Reason}

The following list describes the information displayed:

Category: A Windows PowerShell-defined System.Management.Automation.ErrorCategory constant.
TargetName: By default, the name of the object the cmdlet was processing when the error occurred. Or, another cmdlet-defined string.
TargetType: By default, the type of the target object. Or, another cmdlet-defined string.
Activity: By default, the name of the cmdlet that created the error record. Or, some other cmdlet-defined string.
Reason: By default, the exception type. Or, another cmdlet-defined string.

Replacement Error Message

When you develop an error record for a cmdlet, the default error message for the error comes from the default message text in the System.Exception.Message property. This is a read-only property whose message text is intended only for debugging purposes (according to the .NET Framework guidelines). We recommend that you create an error message that replaces or augments the default message text. Make the message more user-friendly and more specific to the cmdlet.

The replacement message is provided by an System.Management.Automation.ErrorDetails object. Use one of the following constructors of this object because they provide additional localization information that can be used by Windows PowerShell.

ErrorDetails(Cmdlet, String, String, Object[]): Use this constructor if your template string is a resource string in the same assembly in which the cmdlet is implemented or if you want to load the template string through an override of the System.Management.Automation.Cmdlet.GetResourceString method.
ErrorDetails(Assembly, String, String, Object[]): Use this constructor if the template string is in another assembly and you do not load it through an override of System.Management.Automation.Cmdlet.GetResourceString.

The replacement message should conform to the .NET Framework design guidelines for writing exception messages with a small difference. The guidelines state that exception messages should be written for developers. These replacement messages should be written for the cmdlet user.

The replacement error message must be added before the System.Management.Automation.Cmdlet.WriteError or System.Management.Automation.Cmdlet.Throwterminatingerror* methods are called. To add a replacement message, set the System.Management.Automation.ErrorRecord.ErrorDetails property of the error record. When this property is set, Windows PowerShell displays the System.Management.Automation.ErrorDetails.Message* property instead of the default message text.

Recommended Action Information

The System.Management.Automation.ErrorDetails object can also provide information about what actions are recommended when the error occurs.

Invocation information

When a cmdlet uses System.Management.Automation.Cmdlet.WriteError or System.Management.Automation.Cmdlet.Throwterminatingerror* to report an error record, Windows PowerShell automatically adds information that describes the command that was invoked when the error occurred. This information is provided by a System.Management.Automation.Invocationinfo object that contains the name of the cmdlet that was invoked by the command, the command itself, and information about the pipeline or script. This property is read-only.

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